Amazon EC2 instances use SSH keys for authentication via SSH. The private key that you used when deploying the EC2 instances, is the one that you need to use when you SCP between VMs
$ sudo scp -i /path/to/private/key /path/to/source/file user@X.X.X.X:/destination/path
You received an error because the names of tasks isn't set correctly.
To list tasks with the exact names use:
the i at the beginning of tasks name mean that the package is installed, u = task isn't installed.
Here is an example to see the difference between debian and kali (xfce)
On debian: the task name is xfce-desktop
On kali : the ...
I'm not sure that a 1:1 threading model is garunteed in java. That means a java thread may or may not represent an OS thread. It could very well be that several java threads are managed by the java runtime-environment and represented to the OS as a smaller number of threads. It's really implementation specific. I'd recommend a lower-level language (C or ...